PREPARATORY MAPS AND DATA 17 



to make sure of critical points and of the main crossings. It 

 rarely happens that the system of sewer-pipes will lie above 

 the other pipes, and it is necessary, therefore, that they be 

 designed to come enough below to allow at least 6 inches of 

 dirt between the top of the sewer-pipe and the bottom of the 

 water- or gas-pipe. It is awkward to find, just before joining 

 in a lateral that is already laid, that the sewer-grade is of the 

 same elevation as a 1 5-inch water-main, and that the sewer 

 must go over or under and get back to the old grade within 

 50 feet. The old sewers and drains should be incorporated in 

 the survey and mapped with care, since they may be made a 

 part of the new system. They should be thoroughly examined 

 and their condition, grade, and position personally noted and 

 recorded. It may be that a small house-sewe r can be laid 

 inside of an old storm-sewer, saving the 'cost of re-excavation. 



The data for these maps are generally only to be obtained by 

 a survey, which in open and unimproved land may be made 

 at the time of staking out, but under ordinary conditions should 

 be done before, since the information is needed for the staking 

 out. A convenient field-party for this survey is a transit man, 

 two chainmen, and the chief of party, who acts as note-keeper. 

 In one day such a party will, from actual experience, survey 

 from 2000 to 6000 feet of street on both sides, taking plus 

 distances of fence-lines and side lines of houses* (prolonging 

 them by eye across the transit-line), measuring from the transit- 

 line to curb- and street-lines, and pacing to the front lines of 

 houses. The average distance run by such a party in the small 

 city of Ithaca in the summer of 1895 was 4400 feet per day. 

 This work was plotted by one man in six days, making cost of 

 the work, mapped and plotted, about $18.50 per day, or $22.25 

 per mile. 



Additional data as to the cost of surveys such as might be 

 needed for work of this character are given as follows: 



At St. Louis, where the entire cost of a careful survey of 



* For detailed directions of approved surveying methods for locating buildings 

 along a street, see Engineering News, Vol. LIV, pp. 173, 310, 380. 



